1. Field of the Invention
The present invention relates to a fluid pressure actuator. This patent application is based on Japanese patent Application No. 2007-091407. The disclosure of the Japanese Patent Application is incorporated herein by reference.
2. Description of Related Art
A conventional fluid pressure actuator includes: a cylinder containing a piston; a fluid pressure pump which feeds and discharges working fluid to and from the cylinder to move the piston forward and backward; and an electric motor which drives the fluid pressure pump. For the fluid pressure actuator, a fluid pressure pump is suitably used displacement of which is changed by adjusting an angle of a swash plate. A method to reduce the power consumption of the electric motor has been known. In the method, the swash plate is controlled to reduce the angle of the swash plate. Conventionally, a power source such as electric power source or fluid pressure source, other than a power source for driving the piston, is used for the swash plate control.
For example, Japanese Laid Open Patent Application (JP-P2001-295802A) discloses a method in which an electric motor, other than a electric motor for driving a fluid pressure pump, adjusts the angle of the swash plate through a reduction gear, and a method in which displacement is reduced based on pressure difference in a fluid pressure actuator.
Japanese Laid Open Patent Application (JP-P 2005-240974A) discloses a method of controlling the rotation speed of an electric motor for driving a fluid pressure pump and the angle of a swash plate through mapping control based on target and present positions of a piston and an output force of the piston.